Will Colbert bring in younger audience for brands?

George Clooney chats with Stephen Colbert on the premiere of "The Late Show with Stephen Colbert," Tuesday Sept. 8, 2015.

Stephen Colbert's tenure on "The Late Show" has officially begun. But, it wasn't just fans of "The Colbert Report" eagerly awaiting the comedian's debut: Brands have been lining up to get ads.

A source with close knowledge of the situation said that 30-second ad spots during the premiere were going for about $175,000. CBS did not immediately respond to a request for comment.

By comparison, Adweek reported that advertising cost provider SQAD NetCosts placed rates at about $52,000 per 30 seconds for late night leader NBC's "The Tonight Show Starring Jimmy Fallon" in the second quarter of 2015, while "Jimmy Kimmel Live" on ABC was around $24,000. Colbert was pulling in about $50,000 by the time his Comedy Central show went off the air in 2014. Neither NBC nor ABC immediately responded to requests for comment.

Part of what drove the prices up so high was excitement about the potential for a younger audience, especially compared to the crowd former "Late Show" host David Letterman drew. According to marketing firm Magna Global, Letterman's average viewer was 60 years old. The average "Colbert Report" audience viewer was 44.

"It's an opportunity to draw in some younger viewers," said Brian Hughes, Magna Global audience analysis practice lead and senior vice president. "Between Jimmy Fallon taking over 'The Tonight Show' and this, in a way it's revitalizing late night."

Hughes said Fallon's success with driving down the age of late night viewers has encouraged marketers to consider the programs with renewed interest. The NBC show has an average TV viewership age of 54, according to Magna. Kimmel remains a little older at 57. He projected Colbert to average around mid-50s.

While that still may seem a little old for millennial-chasing brands, multiple sources say CBS has reportedly promised the show will have a heavy digital presence. Letterman notoriously shied away from online integration, but Colbert has already proven himself on the medium. YouTube late night viewership skews 18 to 34, Hughes pointed out.

"Considering the way viewing is trending these days, there's interest in what kind of digital afterlife the show can take on," Hughes said. "Not everyone can be awake to watch."

Already, the show has started to reveal a large social media audience. According to data analytics platform Amobee Brand Intelligence, within the first 30 minutes of the premiere episode, there were 19,872 tweets mentioning Stephen Colbert. Thirty-four percent were positive, 54 percent were neutral and just 12 percent were negative.

It wasn't just Colbert that got audiences excited. Oreo and Sabra both benefited from Twitter buzz thanks to nods during the show. (The cookie brand didn't pay for its mention, but Sabra's was due to a paid product placement.) The in-show comments increased the number of tweets about Oreo and hummus by 92 percent and 626 percent, respectively.

But, while a good chunk of Oreo and hummus-related tweets were positive, the firm reported Sabra only pulled in an 18 percent positive rating.

Despite the early buzz, Media Dynamics President Ed Papazian warned against what could potentially just be hype. He wasn't sure if the strategy to switch to younger audiences was a smart one, considering their fickle nature.

"Typically with late night, a small segment watches four or five times a week," he said. "Is Colbert going to be that powerful allure that the 18- to 34-year-olds will become that disciplined? That's the question because the old folks will be driven away."

Papazian said the Colbert's "frenzy" during his premiere episode where he ran around the stage could alienate his audience, especially older viewers who are looking to a show to wind down their day.

"His eyes are bulging," he said. "He's trying too hard. There's a danger of a burnout."

Nor was he sold on whether Colbert could deliver the youthful audience brands wanted. Most notably, he said Colbert faces a big challenge due to the vast difference in lead-in program age. "The Daily Show" had an average age of 47. Colbert's "The Late Show" will be preceded by local news, which skews 55 to 60.

Papazian added even high early numbers don't mean staying power, as evidenced by past late night hosts like Conan O'Brien, Pat Sajak and Merv Griffin. While Tuesday night's "The Late Show with Stephen Colbert" debut had a 123 percent larger audience than last year's season premiere—and was almost twice as large as Fallon viewership that night—he expected to see half that number Wednesday.

The source with knowledge about pricing also noted that they expected the price to drop to about $20,000 to $22,000 during the regular season, about the same price Letterman commanded during his run.

Even Hughes agreed that the audience should drop dramatically and plateau in a few weeks, though he was optimistic that it would still settle down to be a larger audience than Letterman's.

"With Fallon, the sort of halo effect lasted for a few weeks and then leveled out coming ahead of what (Jay) Leno did with young adults," he said. "The interest will still be high."

Disclosure: "The Tonight Show Starring Jimmy Fallon" airs on NBC, which is owned by CNBC's parent company NBC Universal.